http://llvm.org/bugs/show_bug.cgi?id=8233
Summary: Sibcall optimization rejects sret-using functions
Product: new-bugs
Version: trunk
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Sibcall optimization does not take place when 'sret' is used on X86-64. For
example:
=====
$ cat test.ll
; ModuleID = '/home/urxae/.ccache/test.tmp.s010625.15525.ii'
target datalayout =
"e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
target triple = "x86_64-unknown-linux-gnu"
%struct.Foo = type { [3 x i64] }
define void @_Z10tailcallerv(%struct.Foo* sret %agg.result) nounwind {
entry:
tail call void @_Z10tailcalleev(%struct.Foo* sret %agg.result) nounwind
ret void
}
declare void @_Z10tailcalleev(%struct.Foo* sret) nounwind
$ llc test.ll -o -
.file "test.ll"
.text
.globl _Z10tailcallerv
.align 16, 0x90
.type _Z10tailcallerv,@function
_Z10tailcallerv: # @_Z10tailcallerv
# BB#0: # %entry
pushq %rbx
movq %rdi, %rbx
callq _Z10tailcalleev
movq %rbx, %rax
popq %rbx
ret
.Ltmp0:
.size _Z10tailcallerv, .Ltmp0-_Z10tailcallerv
.section .note.GNU-stack,"",@progbits
=====
This despite the fact that the code for tailcaller() here only needs to be a
jump to tailcallee()...
Removing sret from tailcaller() doesn't help, but removing it from both works.
(Note: removing it only from tailcallee() *shouldn't* work, because then
tailcaller() can't copy %rdi to %rax on exit)
32-bit x86 code seems to have this problem as well, by the way.
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